1. Field of the Invention
The present invention relates to communications, and in particular to providing a multimedia subsystem control for supporting emergency services sessions over circuit-switched subsystems and packet subsystems, as well as effecting transfers of established calls from one subsystem to another.
2. Description of the Related Art
Voice sessions or calls can be supported by circuit-switched and packet-based communications. In many communication environments, circuit-switched communications are provided by circuit-switched subsystems while packet communications are provided by packet subsystems. Traditionally, circuit-switched communications have been used for voice communications, and as such, access to emergency services for police, fire, and ambulance services has been provided by circuit-switched subsystems.
As voice services are being deployed over packet subsystems, there is a need to provide support for emergency services for packet subsystem users. Given the existing emergency services infrastructure in the circuit-switched subsystems, network providers are employing techniques to allow the emergency services provided in the circuit-switched subsystems to be accessed by the packet subsystem users.
In wireless communication environments, user elements are mobile, and as such, often move from one location to another. With movement, service for the user element may be transferred from one access point or base station to another within a given subsystem. Many user elements may be served by different types of subsystems, and based on the location of the user elements or a desired application, may transfer service from one type of subsystem to another.
For emergency services, it is important to maintain an emergency services session between an operator and the user element as the user element transfers from one access point or base station within a particular subsystem as well as between different subsystems. Although transfers from one access point or base station to another are handled within the given subsystem, there is a need to efficiently and effectively transfer existing emergency services sessions from one type of subsystem to another.